- ID:
- ivo://CDS.VizieR/J/ApJ/835/152
- Title:
- HST FGS-1r parallaxes for 8 metal-poor stars
- Short Name:
- J/ApJ/835/152
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Hubble Space Telescope (HST) fine guidance sensor observations were used to obtain parallaxes of eight metal-poor ([Fe/H]< -1.4) stars. The parallaxes of these stars determined by the new Hipparcos reduction average 17% accuracy, in contrast to our new HST parallaxes, which average 1% accuracy and have errors on the individual parallaxes ranging from 85 to 144{mu}as. These parallax data were combined with HST Advanced Camera for Surveys photometry in the F606W and F814W filters to obtain the absolute magnitudes of the stars with an accuracy of 0.02-0.03 mag. Six of these stars are on the main sequence (MS) (with -2.7<[Fe/H]< -1.8) and are suitable for testing metal-poor stellar evolution models and determining the distances to metal-poor globular clusters (GCs). Using the abundances obtained by O'Malley+ (2017ApJ...838...90O), we find that standard stellar models using the VandenBerg & Clem (2003AJ....126..778V) color transformation do a reasonable job of matching five of the MS stars, with HD 54639 ([Fe/H]=-2.5) being anomalous in its location in the color-magnitude diagram. Stellar models and isochrones were generated using a Monte Carlo analysis to take into account uncertainties in the models. Isochrones that fit the parallax stars were used to determine the distances and ages of nine GCs (with -2.4{<=}[Fe/H]{<=}-1.9). Averaging together the age of all nine clusters led to an absolute age of the oldest, most metal-poor GCs of 12.7+/-1.0Gyr, where the quoted uncertainty takes into account the known uncertainties in the stellar models and isochrones, along with the uncertainty in the distance and reddening of the clusters.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/707/1347
- Title:
- HST F160W photometry in RMC 136
- Short Name:
- J/ApJ/707/1347
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present deep Hubble Space Telescope NICMOS 2 F160W band observations of the central 56"x57" (14pcx14.25pc) region around R136 in the starburst cluster 30 Dor (NGC 2070) located in the Large Magellanic Cloud. Our aim is to derive the stellar initial mass function (IMF) down to ~1M_{sun}_ in order to test whether the IMF in a massive metal-poor cluster is similar to that observed in nearby young clusters and the field in our Galaxy. We estimate the mean age of the cluster to be 3Myr by combining our F160W photometry with previously obtained HST WFPC2 optical F555W and F814W band photometry and comparing the stellar locus in the color-magnitude diagram with main sequence and pre-main sequence isochrones. The color-magnitude diagrams show the presence of differential extinction and possibly an age spread of a few megayear. We convert the magnitudes into masses adopting both a single mean age of 3Myr isochrone and a constant star formation history from 2 to 4Myr. We derive the IMF after correcting for incompleteness due to crowding. The faintest stars detected have a mass of 0.5M_{sun}_ and the data are more than 50% complete outside a radius of 5pc down to a mass limit of 1.1M_{sun}_ for 3Myr old objects.
- ID:
- ivo://CDS.VizieR/J/ApJ/840/30
- Title:
- HST/Gemini proper motions for Pyxis
- Short Name:
- J/ApJ/840/30
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a proper motion measurement for the halo globular cluster Pyxis, using Hubble Space Telescope/ACS data as the first epoch and GeMS/GSAOI Adaptive Optics data as the second, separated by a baseline of ~5 years. This is both the first measurement of the proper motion of Pyxis and the first calibration and use of Multi-Conjugate Adaptive Optics data to measure an absolute proper motion for a faint, distant halo object. Consequently, we present our analysis of the Adaptive Optics data in detail. We obtain a proper motion of {mu}_{alpha}_cos({delta})=1.09+/-0.31mas/yr and {mu}_{delta}_=0.68+/-0.29mas/yr. From the proper motion and line-of-sight velocity, we find that the orbit of Pyxis is rather eccentric, with its apocenter at more than 100kpc and its pericenter at about 30kpc. We also investigate two literature-proposed associations for Pyxis with the recently discovered ATLAS stream and the Magellanic system. Combining our measurements with dynamical modeling and cosmological numerical simulations, we find it unlikely Pyxis is associated with either system. We examine other Milky Way satellites for possible association using the orbit, eccentricity, metallicity, and age as constraints and find no likely matches in satellites down to the mass of Leo II. We propose that Pyxis probably originated in an unknown galaxy, which today is fully disrupted. Assuming that Pyxis is bound and not on a first approach, we derive a 68% lower limit on the mass of the Milky Way of 0.95x10^12^M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/ApJ/859/38
- Title:
- HST grism obs. of CARLA galaxy cluster candidates
- Short Name:
- J/ApJ/859/38
- Date:
- 08 Mar 2022 13:56:29
- Publisher:
- CDS
- Description:
- We report spectroscopic results from our 40-orbit Hubble Space Telescope slitless grism spectroscopy program observing the 20 densest Clusters Around Radio-Loud AGN (CARLA) candidate galaxy clusters at 1.4<z<2.8. These candidate rich structures, among the richest and most distant known, were identified on the basis of [3.6]-[4.5] color from a 408hr multi-cycle Spitzer program targeting 420 distant radio-loud AGN. We report the spectroscopic confirmation of 16 distant structures at 1.4<z<2.8 associated with the targeted powerful high-redshift radio-loud AGN. We also report the serendipitous discovery and spectroscopic confirmation of seven additional structures at 0.87<z<2.12 not associated with the targeted radio-loud AGN. We find that 10^10^-10^11^M_{sun}_ member galaxies of our confirmed CARLA structures form significantly fewer stars than their field counterparts at all redshifts within 1.4<=z<=2. We also observe higher star-forming activity in the structure cores up to z=2, finding similar trends as cluster surveys at slightly lower redshifts (1.0<z<1.5). By design, our efficient strategy of obtaining just two grism orbits per field only obtains spectroscopic confirmation of emission line galaxies. Deeper spectroscopy will be required to study the population of evolved, massive galaxies in these (forming) clusters. Lacking multi-band coverage of the fields, we adopt a very conservative approach of calling all confirmations "structures," although we note that a number of features are consistent with some of them being bona fide galaxy clusters. Together this survey represents a unique and large homogenous sample of spectroscopically confirmed structures at high redshifts, potentially more than doubling the census of confirmed, massive clusters at z>1.4.
- ID:
- ivo://CDS.VizieR/J/MNRAS/442/1049
- Title:
- HST gz magnitude of NGC 1023 star clusters
- Short Name:
- J/MNRAS/442/1049
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Faint fuzzies (FFs) are a relatively new class of star cluster, first found in the nearby S0 galaxy NGC 1023 by Larsen & Brodie (2000AJ....120.2938L) using Wide Field Planetary Camera 2 (WFPC2) images from the Hubble Space Telescope (HST). Here, we investigate the star cluster system of NGC 1023 using an eight pointing mosaic of Advanced Camera for Surveys (ACS) images from HST. We identify blue and red normal globular clusters (two of which are particularly luminous and dense) and two ultracompact dwarf objects (with effective radius ~10pc). With our more complete spatial coverage, we also find 81 red and 27 blue FFs. We confirm the association of the red FFs with the disc of NGC 1023, consistent with them being long-lived open clusters. Half of the blue FFs appear to be associated with the dwarf satellite galaxy NGC 1023A (which was largely absent from the original HST/WFPC2 coverage), while the remainder are spatially coincident with the densest HI gas that surrounds NGC 1023. The blue FFs have colours that are consistent with young (few 100Myr old) star clusters that formed during the most recent interaction between NGC 1023 and its satellite NGC 1023A.
- ID:
- ivo://CDS.VizieR/J/ApJ/827/89
- Title:
- HST imaging of Pisces A and B
- Short Name:
- J/ApJ/827/89
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present observations of the Pisces A and B galaxies with the Advanced Camera for Surveys on the Hubble Space Telescope. Photometry from these images clearly resolves a red giant branch (RGB) for both objects, demonstrating that they are nearby dwarf galaxies. We describe a Bayesian inferential approach to determining the distance to these galaxies using the magnitude of the tip of the RGB (TRGB), and then apply this approach to these galaxies. This reveals the distance to these galaxies as 5.64_-0.15_^+0.13^Mpc and 8.89_-0.85_^+0.75^Mpc for Pisces A and B, respectively, placing both within the Local Volume but not the Local Group (LG). We estimate the star formation histories of these galaxies, which suggests that they have recently undergone an increase in their star formation rates. Together these yield luminosities for Pisces A and B of M_V_=-11.57_-0.05_^+0.06^ and -12.9+/-0.2, respectively, and estimated stellar masses of log(M*/M_{sun})=7.0_-1.7_^+0.4^ and 7.5_-1.8_^+0.3^. We further show that these galaxies are likely at the boundary between nearby voids and higher-density filamentary structure. This suggests that they are entering a higher-density region from voids, where they would have experienced delayed evolution, consistent with their recent increased star formation rates. If this is indeed the case, they are useful for study as proxies of the galaxies that later evolved into typical LG satellite galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJS/256/40
- Title:
- HST imaging survey of low-z Swift-BAT AGNs
- Short Name:
- J/ApJS/256/40
- Date:
- 03 Mar 2022 00:28:07
- Publisher:
- CDS
- Description:
- We present initial results from a Hubble Space Telescope snapshot imaging survey of the host galaxies of Swift-BAT active galactic nuclei (AGN) at z<0.1. The hard X-ray selection makes this sample relatively unbiased in terms of obscuration, compared to optical AGN selection methods. The high-resolution images of 154 target AGN enable us to investigate the detailed photometric structure of the host galaxies, such as the Hubble type and merging features. We find 48% and 44% of the sample to be hosted by early-type and late-type galaxies, respectively. The host galaxies of the remaining 8% of the sample are classified as peculiar galaxies because they are heavily disturbed. Only a minor fraction of host galaxies (18%-25%) exhibit merging features (e.g., tidal tails, shells, or major disturbance). The merging fraction increases strongly as a function of bolometric AGN luminosity, revealing that merging plays an important role in triggering luminous AGN in this sample. However, the merging fraction is weakly correlated with the Eddington ratio, suggesting that merging does not necessarily lead to an enhanced Eddington ratio. Type 1 and Type 2 AGN are almost indistinguishable in terms of their Hubble type distribution and merging fraction. However, the merging fraction of Type 2 AGN peaks at a lower bolometric luminosity compared with those of Type 1 AGN. This result may imply that the triggering mechanism and evolutionary stages of Type 1 and Type 2 AGN are not identical.
- ID:
- ivo://CDS.VizieR/J/ApJ/853/86
- Title:
- HST large programme on {omega} Centauri. II.
- Short Name:
- J/ApJ/853/86
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this second installment of the series, we look at the internal kinematics of the multiple stellar populations of the globular cluster {omega} Centauri in one of the parallel Hubble Space Telescope (HST) fields, located at about 3.5 half-light radii from the center of the cluster. Thanks to the over 15yr long baseline and the exquisite astrometric precision of the HST cameras, well-measured stars in our proper-motion catalog have errors as low as ~10{mu}as/yr, and the catalog itself extends to near the hydrogen-burning limit of the cluster. We show that second-generation (2G) stars are significantly more radially anisotropic than first-generation (1G) stars. The latter are instead consistent with an isotropic velocity distribution. In addition, 1G stars have excess systemic rotation in the plane of the sky with respect to 2G stars. We show that the six populations below the main-sequence (MS) knee identified in our first paper are associated with the five main population groups recently isolated on the upper MS in the core of cluster. Furthermore, we find both 1G and 2G stars in the field to be far from being in energy equipartition, with {eta}_1G_=-0.007+/-0.026 for the former and {eta}_2G_=0.074+/-0.029 for the latter, where {eta} is defined so that the velocity dispersion {sigma}_{mu}_ scales with stellar mass as {sigma}_{mu}_{propto}m^-{eta}^. The kinematical differences reported here can help constrain the formation mechanisms for the multiple stellar populations in {omega} Centauri and other globular clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/716/712
- Title:
- HST light curves of six SNe and Union2
- Short Name:
- J/ApJ/716/712
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z>1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation.
- ID:
- ivo://CDS.VizieR/J/ApJ/754/4
- Title:
- HST monitoring of flaring stars in the Galactic bulge
- Short Name:
- J/ApJ/754/4
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We utilize the Sagittarius Window Eclipsing Extrasolar Planet Search Hubble Space Telescope/Advanced Camera for Surveys data set for a Deep Rapid Archival Flare Transient Search (DRAFTS) to constrain the flare rate toward the older stellar population in the Galactic bulge. During seven days of monitoring 229293 stars brighter than V=29.5, we find evidence for flaring activity in 105 stars between V=20 and V=28. We divided the sample into non-variable stars and variable stars whose light curves contain large-scale variability. The flare rate on variable stars is ~700 times that of non-variable stars, with a significant correlation between the amount of underlying stellar variability and peak flare amplitude. The flare energy loss rates are generally higher than those of nearby well-studied single dMe flare stars.
